Intraosteal ultrasound during surgical implantation

ABSTRACT

IntraOsteal UltraSound (IOUS) is the use of acoustical energy to facilitate “real-time” manipulation and navigation of a device for intraosseous placement of synthetic or biologic implants and to diagnose the condition of the tissue into which the implant is being placed. Representative applications include placement of synthetic or biologic implants, such as bone screws, through vertebral pedicles during spinal fusion surgery. Devices for use in the placement of the implants include a means for creating a lumen or channel into the bone at the desired site in combination with a probe for providing realtime feedback of differences in density of the tissue, typically differences in acoustical impedence between cancellous and cortical bone. The devices will also typically include means for monitoring the feedback such as a screen creating an image for the surgeon as he creates the channel, and/or an audible signal which different tissues are present. The system can also be used for diagnostic applications.

This applications claims priority to U.S. Provisional Patent ApplicationNo. 60/348,446 filed Oct. 24, 2001.

BACKGROUND OF THE INVENTION

The present invention is generally in the field of methods and devicesfor surgical placement of implants, especially into bone.

Surgical implantation of devices such as screws, pins, and other medicalimplants into bone is frequently the only means to safely immobilize thebone. Typically, this is done by passing a probe through the corticalbone, the dense, hard bone on the outside of bony structures, and intothe cancellous bone, the soft, compliant spongy bone on the inside ofthe bone.

As shown in FIG. 1, the relevant structures are the pedicles 12 andvertebral body 10. These structures are comprised of two types of bone:cortical 14 and cancellous 16. Cortical bone is the dense, hard bonecovering the illustrated structures. Cancellous bone, commonly referredto as “spongy bone” is “soft” and compliant and provides the inner corefor these structures.

Surgeons exploit the difference in these two bone types during pedicularcannulation. When passing a blunt, narrow “probe” through the pedicle,the instrument tip tends to follow the path of least resistance, thecancellous bone. The operator continues to direct this instrument,usually with x-ray assistance, until it has penetrated 50-80% of theanterior/posterior diameter of vertebral body. Successful cannulation isachieved when an intra-cancellous pilot channel is created without abreach of the cortical bone. A breach can injure critical structures inclose proximity, such as spinal cord, nerve root, and vessels. Thelarger the cancellous inner core and the thicker the outer cortex, theeasier the task. This is the case, for example, in the lumbar vertebrae,particularly the L3-S1 pedicles. However, in ascending the spine fromthe lumbar to thoracic and cervical vertebrae, the complexity of thetask increases substantially. Since pedicular cannulation is essentiallya “blind” technique, tactile feedback is critical to the operator duringcreation of the pilot channel. When the boundaries of the bone type arelarge and well defined, as they generally are in the lumbar pedicles,the relatively thick cortical wall and large core of cancellous bonefacilitates intraosteal passage of a blunt tipped probe. Thecortical/cancellous boundary is readily detected as the probe isadvanced. In higher vertebrae, i.e., thoracic and cervical, the pedicledimensions decrease markedly. As the overall cross-sectional diameter ofthe pedicle decreases, so does the cortical wall thickness. As theoperator's tactile sensitivity to the cortical/cancellous boundarydecreases, the risk for breach increases, even with adjunctive virtualimage guidance.

A high complication rate associated with pedicle screw placement inlumbar vertebrae is well documented. As previously stated, the risk iseven higher in thoracic and cervical spine. Placement of pedicle screwsin the certical vertebrae, with the exception of perhaps C2 and C7, isvirtually unheard of. Most posterior fixation procedures of the cervicalspine, therefore, are through screw fixation in the lateral masses; notnearly as strong as pedicular fixation.

Since pedicular fixation in many cases provides for maximum constructstability and strength an alternative and improved method and mode ofnavigation is essential for routine cannulation of these upper vertebralpedicles.

Currently, there is no simple or reliable method to navigate cannulationof vertebral pedicles in vivo and in real time during placement ofimplants. This is a challenging task even in the hands of the mostexperienced spine surgeon, especially in the upper thoracic and cervicalvertebrae. Current modes of virtual guidance are all based on“historical” data and the images upon which the guidance is dependent donot necessarily present the actual anatomic position at any giveninstant in real time an instrument is engaging tissue.

It is therefore an object of the present invention to provide methodsand devices to guide cannulation or other procedures within bone orsimilar types of materials in the body, which are reliable and realtime.

SUMMARY OF THE INVENTION

As defined herein, IntraOsteal UltraSound (IOUS) is the use ofacoustical energy, .e., ultrasound, to facilitate “real-time”manipulation and navigation of a device for intraosseous placement ofsynthetic or biologic implants. Representative applications includeplacement of synthetic or biologic implants, such as bone screws,through vertebral pedicles during spinal fusion surgery. Such implantsare part of a larger “construct” designed to immobilize unstablevertebrae incorporated by it. The purpose of such a construct is topermit bony fusion of those unstable vertebrae that contribute to painor impaired spine function. Devices for use in the placement of theimplants include a means for creating a lumen or channel into the boneat the desired site in combination with a probe for providing realtimefeedback of differences in density of the tissue, typically differencesin density between cancellous and cortical bone. The devices alsotypically includes means for monitoring the feedback such as a screencreating an image for the surgeon as he creates the channel.

IOUS can also be used for measurement of bone thickness, identificationand confirmation of pseudoarthrosis in failed spinal fusions,bone-to-avascular-necrosis interface, guidance of pedicle screws acrossa vertebral body during anterior spinal deformity corrective surgery,and search for osteoid osteoma and vascular lesions such as aneurismalbone cysts, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a thoracid vertebrate (T6) showing the pedicles,corticle bones, cancellous bone, and bone screw trajectory for spinalfusion.

FIGS. 2 a, 2 b and 2 c are diagrams of a device for use in IOUS,including a computer processor, acoustical generator, monitor,articulating arm, and transducer input ports. FIG. 2 a, perspectiveview; FIG. 2 b, side view; FIG. 2 c, top view.

FIG. 3 is a perspective view of a transducer.

FIG. 4 is a perspective view of input means from the transducer to thetransducer input port.

FIGS. 5 a and 5 b are schematics of the process, wherein the computerprocessor processes the input and output from the acoustical generatorand transducer in FIG. 5 a, to produce an image, shown in FIG. 5 b.

FIGS. 6 a-d are perspective views of the instruments used in theprocess. FIGS. 6 a and 6 b are drill bits of a type currently availablemodified to incorporate transducers that provide feedback to create animage as the drill bit creates a pilot hole. FIGS. 6 c and 6 d areperspective views of an instrument that is both a transducer and capableof creating a pilot hole.

DETAILED DESCRIPTION OF THE INVENTION

An IntraOsteal UltraSound (IOUS) based system is used for the placementof implants, both initially and/or as the surgeon is operating, and fordetection and characterization of bone to enable the surgeon todetermine the precise location to begin surgery to place the implant, aswell as to determine the condition of the tissues into which the implantis to be placed.

The system includes a device for sensing and alerting via an auditory orvisual signal the absence of bone (cortical, cancerous, cartilaginous)i.e., as would be the case of a bony non-union (pseudoarthrosis),fracture, neoplasms, avascular necrosis, vascular lesions, etc. Suchabnormalities will have acoustical properties with echogenicity widelydisparate from all normal bone types. The IOUS provides a means toqualitatively recognize or delineate abnormal regions, to insure thatany implant being guided and placed is done so in bone of a normalcaliber (density, homogeneity, architecture, etc.). The frequency rangeof bone is such that any quantifiable signal falling outside of aparticular range will produce an alert signal that is different thanthat of a signal produced with normal bone. This is important whennavigating from one bony structure to another bony structure across anon-bony interface, i.e., as in joints, especially when implanting facetscrews, hip pins, etc.

Effective deployment of IOUS can be predicated on a multiple number offactors or variables that are unique to bone, including:

-   -   1. Bone mineral density (BMD).    -   2. Histology of bone;    -   3. Bone disease or degeneration    -   4. Water content (blood, bone marrow, etc.).    -   5. Cartilage composition.

In its totality, bone, in all of its iterations, combinations andarchitecture, has a distinct “signature”. It's echogenicity, modes ofattenuation, scattering coefficients, and other characteristics willalways be quite distinct from other soft tissues of the. The array ofacoustical properties, i.e., frequency, bandwidth, attenuationcharacteristics, amplitude, scatter coefficients, will all be unique foreach type of bone. Effective navigation involves not only delineatingcortical bone from cancellous bone but the integrity of those elementsas well.

I. Implants

A number of different types of implants can be placed using the devicesdescribed herein. In the simplest embodiment, the implant is a titaniumscrew or pin which is implanted into a channel created by channeling aprobe through the cortical bone into the cancellous bone within the boneto be immobilized.

In the preferred embodiment, the bone is a vertebral body and channelsare created within the pedicles of adjacent vetebral bodies which arethen screwed together. Simply put, this spine construct is analogous toa splint or cast placed on or around long bone fractures until healing(fusion) occurs. Screws can be removed after the bone has healed.

Other implants that can be used include pedicle screws and hip pins.Implants may be formed of metal, ceramic, polymer, biological materials(including bone), and combinations thereof.

II. Devices That can be Used to Image the Area

Devices include at a minimum a probe for moving within the tissue to beimaged and means for applying and/or receiving ultrasound or acousticenergy, and means for transmitting data to an external monitoring means.Optionally, the devices also including means for placement of theimplant, and signaling devices that generate a signal when the probecrosses from one type of tissue to another.

Ultrasound is a form of energy that is quantifiable, reliable,non-ionizing, and relatively inexpensive. The different acousticalproperties of cortical and cancellous bone make it amenable to real timeinterrogation and delineation during instrument manipulation. There aretwo modes by which acoustical energy that is emitted and received invivo could be utilized for reliable guidance:

1. Visual (Radar): Though a small transducer mounted on or within anarrow instrument, emission of a predefined acoustical signal, can, uponreflection, be electronically processed to present the disparatesignals, altered by the marked difference in echogenicity of corticaland cancellous bone, into a visual graphic image displaying therelationship of the instrument tip with respect to thecortical/cancellous tissue in both the axial and sagital planes.

2. Auditory (Sonar): By a process similar to the above, the alteredsignal can be processed such that when a given threshold is met, e.g.,when the instrument tip is in direct contact with cortical bone, anaudible tone can be generated alerting the operator of an impendingbreach if he were to continue the manipulation at the presenttrajectory.

3. Dual Visual/Auditory: By blending the benefits of both, the operatorhas constant feedback that would enhance accuracy and efficiency ofcannulation.

III. Methods for Detection and Characterization of Bone

The ultrasound is used to measure or provide analysis of one or morefactors or variables, including

1. Bone mineral density (BMD);

2. Histology of bone, i.e., cancellous which is trabecular versuscortical which is lamellar;

3. disease such as osteoporosis, calcification, pseudoarthrosis orarthritis;

4. water content (blood, bone marrow, etc.);

5. cartilage composition;

6. lesions, vascular defects, neoplasms, or avascular necrosis.

This information assists in knowing the integrity (ex. normal BMD, lowBMD) of where one is going as well as the location (ex. cortical tocancellous) one is going to.

FIGS. 2 a-2 c represent a system 20 for use as described herein. Thesystem 20 includes a computer processing unit (“CPU”) 22, articulatingarm 24 connecting a monitor 26 to the system 20, a monitor 26, anacoustical generator 28, and transducer input port 32. In a preferredembodiment, the system 20 can be rolled on rollers 30 to the operatingroom. In another preferred embodiment, the articulating arm 24 allowsfor a complete 360 degree rotation and height adjustment by the surgeon.

The transducer 34 is shown in more detail in FIG. 3. The transducer 34includes input and output connections 36 and a probe 38, typicallybetween about 2 and 4 mm in diameter. The transducer emits signals at adefined bandwidth and frequency which is conveyed to and from theinput/output connections 36 to the system 20 via the input port 32.

The signals are processed by the CPU 22 to generate signals (FIG. 5 a)sent to the monitor 26, which then displays an image of the tissue theprobe 38 is passing through. The image 40, shown in FIG. 5 b, indicatesthe cortical interface as a black area 42, and the cancellous tissue asa white area 44. Both radial and sagittal scans can be used to image thetissue, and to provide measurements in real time of the tissue beingimaged.

Two general types of instruments can be used to create the images andpilot holes for the surgeon. These consist of instruments such as thedrill bits currently in use, modified to include a transducer, as shownin FIGS. 6 a and 6 b, and instruments wherein the transducer includes ameans of creating the pilot hole, as shown in FIGS. 6 c and 6 d. Thelatter may be made by modifying existing ultrasound probes to include ahard pointed end. FIG. 6 a shows a hollow drill bit 50, with a burr 52for creating the hole, typically 4-5 mm in height and about 2-4 mm indiameter, a side scan port 54, a lumen 56, and end for connection to theinput/output means 36. FIG. 6 b shows a hollow drill bit 60, throughwhich the transducer 38 can be introduced through the hollow lumen 62,and visualize the area through side port 64 or forward slot 66.

FIG. 6 c shows a “joystick” type of instrument 70. The diameter 72 isbetween 4 and 8 mm, typically, with an interior lumen diameter 74 ofbetween 2 and 4 mm. There is a side scan port 76 and forward view port78. A handle 80 directs the drill 82 through the lumen to create thepilot hole in the bone.

FIG. 6 d shows a transducer 84 for use in scanning and drilling a pilothole. The drill bit 86 is about 2-7 mm in diameter. The input/outputmeans 88 connects to port 90.

IOUS can be used to determine the initial starting location that isoptimal for introduction of an implant. For example, the transducer isplaced on the lamina and used to detect and characterize the boneinterface where the implant is to be positioned.

IOUS can be used to navigate through the bone as the surgeon preparesthe site for implantation, detecting changes from cortical to cancellousto cartilaginous areas, detecting bone to bone unions, and more clearlydefining the area in which the implant is to be placed. For example,IOUS can be used to guide the placement of screws during guidance ofpedicle screws across a vertebral body during spinal fusion or duringanterior spinal deformity corrective surgery.

Further, IOUS can be used as a diagnostic, for measurement of bonethickness, identification and confirmation of pseudoarthrosis in failedspinal fusions, detection of bone-to-avascular-necrosis interface,detection of fractures, and search for neoplasms, osteoid osteoma andvascular lesions such as aneurismal bone cysts, etc. In general the sameequipment and analytical techniques will be used as for surgicalplacement.

1-23. (canceled)
 24. A probe comprising a transducer and a receiver forultrasound or audio signals, wherein the probe is suitable for insertioninto bone.
 25. The probe of claim 1 wherein the signals are selectedfrom the group consisting of frequency, bandwidth, attenuationcharacteristics, amplitude, and scatter coefficients.
 26. The probe ofclaim 1 for emitting and receiving radar.
 27. The probe of claim 1 foremitting and receiving sonar.
 28. The probe of claim 1 furthercomprising means for receiving and transmitting a visual signal.
 29. Theprobe of claim 1 further comprising means for receiving and transmittingan audio signal.
 30. The probe of claim 1 comprising input and outputconnections.
 31. The probe of claim 1 wherein the probe is between twoand four mm in diameter.